This invention relates to a chassis for accommodating an electronic apparatus with a display monitor used in computer systems or the like, and, more particularly, to the quake-proof structure of such a chassis.
Display monitor apparatuses such as CRT display monitor apparatuses (hereinafter referred to as CRT apparatuses) have become widely used, from home to office, because they display the image of an object. CRT apparatuses serve not merely as input/output terminals but are also used as monitors in computer systems and plant equipment, so that their importance is increasing. With the increase of the scope of application and the importance of CRT apparatuses, it has become more important to improve their adaptability to environments and also their reliability with respect to low frequency vibrations such as those engendered by an earthquake.
A CRT apparatus comprises a CRT and various other components. These components have respective frequencies of natural vibration which are determined by their shape, weight, etc. Problems arise when a vibration applied to the CRT apparatus has the same frequency as the natural vibration frequency of a component. In this case, the component resonates with the applied vibration, resulting in the generation of about 20-30 times the applied vibratory force.
Heretofore, vibration-proof members, e.g., vibration-proof rubber pieces, have been used to prevent the applied vibratory force from being amplified due to resonation of components with the applied vibration. With this vibration-proof member, it is necessary to make t/s smaller than the square root of 2 with respect to the transmission function, where s is the natural vibration frequency of the component (or the applied vibration frequency), and t is the vibration frequency of the vibration-proof member. Where this value is adopted, however, the vibration-proof member is very soft, and in the absence of vibration of the CRT apparatus is somewhat precariously unstable. For this reason, the value of t/s is actually set to form 2 to 4 in practice. With these values, however, sufficient effects can not be obtained with respect to low frequency vibrations such as an earthquake, although sufficient effects can be obtained with respect to high frequency vibrations of rotors or the like.
The frequency components of earthquake waves are centered in the range of from 0 to 30 Hz. In the prior art CRT apparatuses having components accommodated and mounted in a chassis, the frequency of natural vibration on the chassis is a round or below 30 Hz, as shown in the depth direction vibration response curve of FIG. 1A and in the width direction vibration response curve of FIG. 1B. These frequencies are or are nearly coincident with the main frequency components of earthquake waves. The main frequency of natural vibration of the CRT apparatus in the vertical direction is slightly higher as shown in FIG. 1C, thereby posing fewer problems. The prior art CRT apparatus chassis described above is equipped with no protective means against vibrations in the depth and width directions, such that, given its natural vibration frequencies are low, it resonates with low frequency vibrations such as those of an earthquake, consequently, adversely affecting the accommodated components. Thus, when low-frequency vibrations such as those of an earthquake are applied to the CRT apparatus, although the accommodated components may not resonate owing to the difference between their natural vibration frequencies and the main frequencies of an earthquake, the CRT apparatus may break or failure of its normal operation may result. Further, physical injury to the operators is a distinct possibility.